A major goal of the neurosciences is to understand how normal intact nervous systems function. One of the ways that the behavioral function of the mammalian brain has been studied is by experimentally damaging or removing some structure within it and examining consequent alterations in behavior. We are exploring the use of genetic techniques as another experimental approach to the investigation of animal brain function. Genes that produce anatomical brain differences between behaviorally "normal" inbred strains of house mice provide a chance to explore the functioning of intact nervous systems, as well as offering possible subtle, precise alterations that are not experimentally achievable in any other manner. We are studying genetic variations in the number of nerve cells in three interconnected cell groups (granule cells of the dentate, and pyramidal cells of regio superior and regio inferior of the hippocampus) within the Ammon's horns (area dentata and hippocampus) of house mice. Our work so far has demonstrated that the mouse Ammon's horn has at least five genetic divisions. This application proposes to continue the descriptive genetic and anatomical studies of Ammon's horn. An additional objective is the creation of appropriate neurogenetic mouse stocks for the determination of behavioral consequences of genetically-associated anatomical variation.